Extending biochemical studies of progesterone receptor components to the mammalian uterus is an important step in understanding the reproductive endocrinology of the normal and abnormal (diseased) uterus. Thus the specific aim of this research proposal is the biochemical characterization of the individual molecular forms of the mammalian progesterone receptor and an evaluation of the relationships between progesterone receptor structure and function. Conventional methods of protein purification will be used to characterize the cytosol and nuclear form(s) of the rat utuerus progesterone receptor. These studies will capitalize on a procedure previously developed in this laboratory which provides quantitative recovery of the labile receptor protein. Additionally, the holoreceptor and/or its subunits will be analysed by electrophoresis under denaturing conditions and reconsititution on nitrocellulose paper. The receptor component(s) detected by these methods will be compared to those of the chick oviduct, to date the only system in which receptors have been extensively characterized. Once the individual molecular species of the mammalian progesterone receptor have been fully characterized, we will examine the relationships between receptor structure and function. These studies will include evaluation of whether estrogen differentially stimulates progesterone receptor components as well as which receptor forms are replenished 12h after progesterone treatment. Additonally we will determine whether the depression of uterine progesterone receptor content 24h after progesterone treatment is expressed in all the receptor forms. Finally, we will determine the physiological and biochemical significance of the nuclear receptor forms, including a unique nuclear fragment observed in preliminary studies. These studies will include an assessment of whether this small nuclear receptor form is generated prior to or subsequent to the initiation of biochemical events in the nucleus and what role, if any, it plays in these events. Experiments will also be directed to assessing whether this nuclear receptor fragment is generated by a physiologically important intranuclear protease. The composite of these biochemical and physiological investigations will provide an excellent basis for further studies of the roles of progesterone receptors in mammalian systems.